In June 1957, Disneyland in California added a new building to Tomorrowland, its vision of a carefree world to come. Made of plastic, the House of the Future looked suitably avant garde and was entirely mechanised. Sponsored by Monsanto, then one of the world’s biggest chemical companies, it attracted 20 million visitors over the next 10 years.

However, as Mathieu Asselin points out in his book Monsanto: A Photographic Investigation, a very different vision of the future was unfolding in Anniston, Alabama. There, since the 1920s, Monsanto had been producing PCBs, chemicals widely used in the creation of lubricants, inks, paints and electrical equipment. PCBs were banned in the US in 1979 due to fears about their toxicity, but the damage to Anniston had already been done. Between 1929 and 1971, some 27 tonnes of PCBs were released into the atmosphere, 810 tonnes flushed into Snow Creek canal, and 32,000 tonnes deposited in an open-air landfill site near the city centre, according to a 2005 report by the Environmental Protection Agency.

PCBs linger long in the environment and have been detected in water far from their original source of release. Prolonged exposure causes skin rashes in humans and changes in blood and urine that may denote liver damage. In 2013, the International Agency for Research on Cancer classified dioxin-like PCBs as human carcinogens.

This postcard of the Monsanto factory in Anniston appears in Asselin’s book. Photograph: Courtesy of the artist

“I began the book seven years ago and I have often been shocked by what I have uncovered,” says Asselin. Using a mixture of his own photographs, archive material, court files, Monsanto’s own adverts and the stories of campaigners and ordinary citizens, his hard-hitting volume, which is shortlisted for this year’s Deutsche Börse photography prize, attacks Monsanto’s reputation and its practices. His approach is unapologetically crusading. “I am playing with fire for sure,” he says.

Asselin’s often low-key landscapes show a town in decline: empty buildings, abandoned businesses, dilapidated houses overgrown by trees and weeds. His equally melancholy images of local residents include one of David Baker, 65, head bowed by his brother’s grave. The caption reads: “Terry Baker died at the age of 16 from a brain tumour and lung cancer, caused by PCB exposure. The average level of PCB in Anniston is 27 times higher than the national average.”

In February 2003, residents of Anniston won a $700m (£491m) settlement from Monsanto in a now-famous court case in which they argued the multinational was responsible for polluting the town and harming its citizens – and that the company had been aware of the toxic effects of PCBs on human health and the environment for decades, but had done nothing about it. In 2007, high pollution levels from PCB dumping were still being recorded in the nearby Snow and Choccolocco creeks. In one 2012 photograph by Asselin, the water at Choccolocco creek appears to be red.

As Asselin’s book makes clear, the 2003 settlement was just one relatively small legal skirmish in a much larger and longer battle that has pitted a global chemical corporation against communities across America and the globe. That ongoing battle sheds light on a US lobbying system that skews the democratic process and often results in politicians, scientists and experts siding with Monsanto against farmers and communities.

“In America,” says Asselin, “the company funds both the Democrats and the Republicans. They don’t have a political standpoint, they just need to make sure everything is OK to make more money. This is the bigger point I am making – global business just cannot go on like this. It has to change.”

Asselin’s gaze shifts from Alabama to Vietnam where, during the long war against the Viet Cong, US troops sprayed 123m gallons of Agent Orange over huge swathes of the country between 1965 and 1971. Asselin cites evidence that about 10% of South Vietnam was contaminated and that between 2.1 and 4.8 million Vietnamese were directly exposed.

Monsanto was one of the producers of the highly toxic defoliant, which is now linked to cancer and birth defects among the Vietnamese population, as well as physical and psychological issues affecting returning US servicemen. One arresting portrait is of Heather Bowser, a woman born with several fingers and part of her right leg missing. Another is a closeup of her deformed hand holding a photograph of her late father, Morris, who served in Vietnam and whose own myriad health problems were directly linked to exposure to Agent Orange.

Asselin’s installation at the Photographer’s Gallery in London, where the work of the four Deutsche Börse finalists is on show, includes two wall-mounted tablets that have Deutsche Börse apps installed so that they can livestream the daily stock market prices of Monsanto and Bayer. (In 2016, Bayer announced that it was planning a $66bn takeover of Monsanto.) This should please the sponsors of the prize no end, I suggest.

“I have to handle the nomination carefully,” says Asselin. “It is a recognition from my fellow artists and professionals – but it is also a prize sponsored by another big multimillion dollar company.” When I mention the Syngenta photo award, which purports to address issues of sustainability while being sponsored by a global pesticide manufacturer, he says: “It’s the biggest bullshit around.”

Asselin is a breath of fresh air in a contemporary photography world where conceptual ambiguity too often undercuts social or political commitments. “I often don’t understand what photographers are trying to tell me,” he says, “so I try to make sure there is no room for ambiguity in my work. I want to make clear exactly what the problem is. There is just no time to waste being neutral.”